The present invention relates generally to a thermoplastic material reinforced with a highly filled composite core layer. The reinforced thermoplastic material is a multilayer structure which comprises a reinforcing core layer and two outer layers of a thermoplastic resin adhered either directly or indirectly to said core layer. The reinforced thermoplastic material may be used, for example in the form of flat sheets, in construction and manufacturing to provide a flat rigid outer surface for various appliances, building panels, vehicles, etc. or may be initially prepared in the form of, or subsequently fabricated into, a variety of shaped articles.
In U.S. Pat. No. 4,044,188 there is disclosed a stampable thermoplastic sheet material reinforced with a central core of a multi-length fiberglass mat. A highly loaded thermoplastic resin also containing short reinforcing fibers in the form of a sheet material is laminated to both major surfaces of a glass mat or its equivalent to fuse and laminate the two sheets and the glass fiber web or mat into an integral sheet construction. Disadvantageously, the previously known structural sheet materials disclosed in the foregoing patent have been found to possess undesirable features. In particular, in applications involving thermocycling wherein the structural sheet material is repeatedly exposed to extreme low temperatures followed by heating to elevated temperatures, the highly expandable thermoplastic layers exert sufficient stress that failure of the central core layer and/or delamination is often the result.
An additional problem associated with structures of the prior art is the tendency of the resin to migrate into the glass mat under molding conditions thereby producing an undesirable surface appearance. To overcome this tendency various fillers may be included into the resin in order to increase the melt viscosity thereof. Disadvantageously the addition of such fillers can adversely affect the physical properties of the thermoplastic layer particularly the impact strength thereof. Also this procedure does not solve the fundamental problem of glass mat layer failure.
While it might be thought possible to control the thermal expansion characteristics of a thermoplastic resin by including reinforcing fibers in the resin itself, such approach has not proven effective in practice. The presence of fibers in the resin layer may generate undesired surface asthetics and cause a reduction in impact strength.
Composite papers are previously known in the art. A suitable technique for their preparation has been disclosed and claimed in U.S. Pat. No. 4,225,383. One commercial use for composite paper is as the backing layer of vinyl flooring materials. In these materials one surface of the composite paper is coated with a polyvinylchloride resin layer.
It would be desirable if there were provided improved reinforced thermoplastic articles having improved resistance to failure due to thermal cycling and having improved dimensional stability. Further, it would also be desirable if such features could be achieved without the attendant substantial adverse effects on impact strength and/or other significant physical properties which are conventionally associated with the use of relatively high loadings of inorganic fibers and/or fillers within various known thermoplastic resin compositions.